1. Field of the Invention
This invention relates generally to the field of magnetic data transducers and methods for manufacturing such transducers, and more particularly to a process for producing a write element in a magnetoresistive (MR) read/write head having special utility in conjunction with shared, or merged, shields on magnetoresistive read/write heads.
2. Description of the Related Art
Magnetoresistive ("MR") heads for disk and tape media comprise separate read and write head elements formed over each other and generally sharing certain common material layers. The read element usually consists of an alloy film such as nickel-iron ("NiFe") that exhibits a change in resistance in the presence of a magnetic field spaced between shielding layers which protect the MR elements from other magnetic fields, such as those from the associated write head element or adjacent written track fields.
The write head element of an MR head is designed much the same way as a thin-film inductive head. It generally comprises two magnetic-pole pieces that are typically made of permalloy, a soft magnetic material. These pole pieces have spaced pole tips and are connected to either at the ends opposite the tips. A deposited-layer copper coil is formed around one of the pole pieces. When an electrical current is supplied to the coil, the connected pole pieces act as an electromagnet core producing a magnetic field across the gap between the two spaced tips of the pole pieces which are held adjacent the recordable magnetic media surface. The magnetic fringe field associated with that gap is used to write data onto the magnetic storage media (disk or tape) by reversing the direction of the magnetic fields on the media surface. The number of turns in the write head coil may be as few as ten or less and the lower inductance this affords over the greater number of turns required in conventional thin-film heads makes it easier to write the signal to the media at very high data frequencies.
Conventionally, thin film heads for both disk and tape media have traditionally maintained the width of the top pole narrower than the width of the shared or bottom pole so that it fits in its entirety on top of the shared or bottom pole. This results, however, in magnetic field contours which are curved outward around the edges of the narrower top pole.
Write operations occur at the trailing or top pole of the write head because the field generated by the head in front of the write gap can change the direction of the magnetization of the media when the media is in front of the gap. Resultantly, there exists a region in front of the gap where the field generated by the head exceeds the coercivity of the media. This is commonly referred to as the "write-bubble". The track width is the width of this bubble transverse to the direction of relative motion between the media and the head. If the direction of the field generated by the head changes, it will change the direction of magnetization of the section of the media that is inside this write-bubble. As the magnetic media moves away from the gap, it is no longer influenced by the field generated there, so the direction of magnetization in the media will remain the same as it is when it leaves the write bubble. Therefore, the shape of the field contour and the field gradient are most critical over the trailing edge pole, i.e. the top pole, since that is where the magnetization in the media is set. Since writing, or encoding, of data occurs as the media moves past the region of the trailing edge of the top pole, the written transitions are curved at the track edges.
On typical MR heads, the write and read elements are separate, but utilize a common shared pole. The trailing edge pole is the top pole of the write element. The bottom pole of the write element is the shared shield. This shared shield is also one pole sandwiching the MR element, with a bottom pole being the shield on the other side of the MR element.
Since the track width is determined by the write element width and more particularly by the width of the trailing, or top pole, the active shape and dimensions of this top pole are critical As head size continues to decrease in an effort to achieve higher and higher data storage capacities, the accuracy requirements for pole tip width continues to increase. Recently, formation of a stepped pole tip configuration on the shared shield has been used in order to reduce fringing. Such a fringing enhanced write transducer is disclosed in U.S. patent application Ser. No. 08/461,411 filed Jun. 5, 1995, and hereby incorporated by reference in its entirety.
The top pole tip width of the MR head essentially determines the track width. The alignment of the top pole with the stepped pole tip on the shared shield also affects the track width. In order to optimally minimize the track width, the difference between the top pole width and the shared shield pole tip width should be close to zero. In addition, the top pole needs to be accurately aligned with the stepped pole tip on the shared shield. As head size continues to decrease, and thus top pole width continues to decrease, the effect of alignment errors between the poles become an even more important consideration in minimizing the track width. Therefore there is a need to ensure correct alignment between the stepped shared pole and the top pole.
One solution has been to deposit the top pole and then use the top pole as a template for ion milling the stepped pole tip of the shared shield. This method has the disadvantage of depositing ablated shared shield material at undesirable locations, such as on the sides of the gap material and the top pole. Thus there is a need for a way to accurately align the top pole with the stepped pole tip on the shared shield without the undesirable deposition of ablated material and additional ion milling steps.